Conventional circuits may include one or more amplifiers to amplify a respective input signal. In general, an amplifier is an electronic device to increase the power or magnitude of a signal (a time-varying voltage or current). An amplifier typically uses electric power from a power supply to amplify the amplitude of a received signal to produce a respective amplified output signal. An amplified output signal can be used for any of multiple purposes such as drive an audio speaker, display screen, etc.
One type of amplifier is an operational amplifier. An operational amplifier (or sometimes referred to as an op-amp) is an Integrated Circuit (IC) that operates as a voltage amplifier. An op-amp has a differential input. That is, it has two inputs of opposite polarity. In certain instances, an op-amp has a single output and a very high gain, which means that the output signal is much higher than input signal. External passive components such as resistors, capacitors, etc., can be coupled to the operational amplifier to control its behavior and provide a desired output.
One attribute of an operational amplifier is its input referred offset voltage, which potentially cause amplification errors if it is a high value. Ideally, the input referred offset voltage associated with an operational amplifier is zero.
In conventional power management IC design, three common methods are used to correct input referred offset of a respective operational amplifier. For example, conventional methods include:
1.) Using large resistor chain as well as iDAC to minimize input referred offset. The disadvantage of this method is large space consumption; moreover, the trim process will also add cost to manufacture.
2.) Using an auxiliary amplifier to sensing/correcting the input referred offset voltage of targeting amplifier. The disadvantage of this method is each targeting amplifier needs an auxiliary amplifier which leads to large space consumption and design complexity; moreover, as the auxiliary amplifier need to be operated between auto zero phase and amplification phase, it requires a dedicated clock circuit.
3.) Using a chopping method in which the polarity of an input signal to the target amplifier needs to be constantly changed. The disadvantage of this method is the required change in polarity; it also requires a filter to be designed to filter out the switching noise.